Known portable sawmills generally employ a pivoting mechanism where the circular sawblade is able to be oriented in either of two operative positions, namely upright and horizontal, and pivoted therebetween. This is referred to as a “swing blade” sawmill. This enables the sawmill to make longitudinal cuts in the felled log to convert it to elongate pieces of milled timber.
Portable sawmills generally use four-stroke engines. Four-stroke engines are preferable to two-stroke engines because two-stroke engines are loud and vibrate and are therefore less pleasant to work with than four-stroke engines, given that the operator is close to the engine. Additionally, it is not easy to accurately govern revolutions per minute in a two-stroke motor. Governing is important firstly because of the extremely high gyroscopic forces which act on the sawblade when rotating the sawblade between the two operative positions. Secondly, governing is required to set the output speed to match the sawblade manufacturer's recommended blade operating speed. Thus, in a portable sawmill, two-stroke motors also require belts and pulleys to reduce revolutions per minute (rpm) to suit the manufacturer's recommended rpm for the sawblade. The belts and pulleys add to the cost and weight for a portable sawmill. Additionally, two-stroke motors have low fuel efficiency.
Electric and hydraulic motors have also been used as power sources for portable sawmills. However, electric and hydraulic motors require external power sources which limit portability. They also require a gantry arrangement in order to route the electrical or hydraulic conduits to the motor. Such arrangements add complexity of the structure. They increase operating risk and affect manoeuvrability of the movable saw head.
Therefore, four-stroke motors are typically the motor of choice for a portable sawmill. However, four-stroke motors have other deficiencies in their application to portable sawmills. Typically, the type of four-stroke engines which are available for agricultural and other low cost applications utilise a carburettor and an engine lubrication system with a wet sump. Both of these features require the four-stroke engine to be maintained at a substantially level orientation. Due to these constraints, it is usual for a portable sawmill to use a four-stroke engine that has a power transfer including a centrifugal clutch and a belt drive which drives the pulley on a 90° gearbox. The output of the 90° gear box is coupled to the sawblade. In order to rotate the sawblade from the horizontal to the vertical position, the sawblade and the gearbox are mounted on a swing plate which can be rotated about the pivot axis of the pulley. This configuration allows the four-stroke engine to remain in a substantially level configuration irrespective of the position of the sawblade. However, the belt drive and gearbox merely add to the cost and weight of the portable sawmill. Additionally a known portable sawmill, the Lucas Mill sawmill, uses 4 cast parts for the swing plate and the gearbox giving rise to manufacturing complexity.
Other more complex engines are also known which use a dry sump which is a separate compartment from the crankcase. These arrangements are more complex and costly to manufacture and therefore add to the cost of an item of agricultural machinery intended to have a low cost base.
It is therefore an object of the present disclosure to provide a portable sawmill which reduces the weight and/or complexity and/or number of components. It is also an object of the present disclosure to provide a portable sawmill which provides the public with a useful choice over known portable sawmills.
Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.